Introducing Tag Strings: Enhancements to Python's F-Strings

PEP 750 – Tag Strings For Writing Domain-Specific Languages | peps.python.org 🔗

This PEP introduces tag strings for custom, repeatable string processing. Tag strings are an extension to f-strings, with a custom function – the “tag” – in place of the f prefix. This function can then provide rich features such as safety checks, lazy ...

PEP 750 introduces tag strings as an enhancement to Python's f-strings, allowing for customizable and repeatable string processing through a tag function. These tag strings enable features like lazy evaluation and safety checks, making them suitable for creating domain-specific languages (DSLs) in web templating and other applications. The proposal aims to overcome limitations of f-strings, such as eager evaluation and lack of intercepting interpolated values, by allowing developers to process the string and its interpolated values before final combination. The PEP includes examples, motivations, and specifications for implementing tag strings, highlighting their potential to improve string handling in Python.

Tag strings are an extension of f-strings with customizable tag functions.
They provide lazy evaluation, safety checks, and support for DSLs.
The proposal addresses limitations of f-strings like eager evaluation and lack of value interception.

What are tag strings?

Tag strings are a new feature in Python that extend f-strings, allowing developers to define custom functions that enhance string processing capabilities, such as lazy evaluation and safety checks.

How do tag strings improve upon f-strings?

Tag strings allow for the processing of both the literal string and interpolated values before combining them, overcoming the limitations of f-strings that evaluate expressions eagerly and do not permit interception of values.

What is the main motivation behind introducing tag strings?

The motivation is to create a more flexible and powerful string processing system in Python, enabling the development of domain-specific languages (DSLs) and providing better control over string formatting and safety.